1. Field of the Invention
This invention relates to a semiconductor device having metal silicide films formed on a gate electrode and source and drain regions and a method for manufacturing the same.
2. Description of the Related Art
In a CMOS semiconductor device, metal silicide films, for example, Ni silicide films are formed in a self-alignment manner on the gate electrode and source and drain regions and the operation speed is enhanced by lowering the wiring resistances thereof. For example, this is disclosed in T. Ohguro et al. “Analysis of Anomalously Large Junction Leakage Current of Nickel Silicided N-type Diffused Layer and Its Improvement”, Extended Abstracts of the 1993 International Conference on Solid-State Devices and Materials, 1993, pp. 192–194.
After formation of the Ni silicide films, contact holes which reach the source and drain regions are formed in an inter-level insulating film in order to form contact plugs. In a case where the contact holes are formed, the junction leakage characteristic will be degraded when the Ni silicide films and portions of the source and drain regions which lie under the Ni silicide films are etched by a reactive ion etching (RIE) process.
In order to prevent the junction leakage characteristic from being degraded, a method for forming a contact liner film having a high selective ratio with respect to the inter-level insulating film on the entire surface containing the silicide films before the inter-level insulating film is formed is used. Then, the etching process is performed in two stages, that is, the inter-level insulating film and the contact liner film are separately etched to form contact holes. Generally, a silicon nitride film is used as the contact liner film.
Particularly, in an NMOS transistor region of a CMOS semiconductor device, there occurs a problem that the Ni silicide films formed on the source and drain regions are liable to be etched at the stage of a wet process which is a process performed before formation of the contact liner film. If the Ni silicide film is etched, the sheet resistance of the Ni silicide film increases and junction leakage occurs. Further, the contact liner film formed on the Ni silicide films on the source and drain regions is liable to be separated. If the contact liner film is separated the separated contact liner film causes dust, thereby making it difficult to perform the integration process after this.
Thus, in a conventional CMOS semiconductor device, there occurs a problem that the Ni silicide films formed on the source and drain regions of the NMOS transistor region are liable to be etched. Further, there occurs a problem that the contact liner film formed on the Ni silicide films on the source and drain regions tends to be separated. Conventionally, it is desired to solve the above problems.